Typically, button cells have a housing composed of two housing halves, a cell cup and a cell lid. These parts can be manufactured using nickel-plated sheet metal to deep draw and obtain punch drawing parts, for example. Conventionally, the cell cup has a positive polarization and the cell lid has a negative polarization. Different types of electrochemical systems can be contained within the housing, for example, zinc/manganese oxide, zinc/air, silver oxide/zinc, mercury oxide/zinc, primary and secondary lithium-ion systems, or secondary systems like nickel/cadmium or nickel/metal hydride.
The electrodes of such electrochemical systems are in general composite electrodes including particles made of an electrochemically active material, a binder and, optionally, a particulate and conductivity enhancing constituent, like carbon black. The binder provides for mechanical resistance of the electrode, in particular the binder is to ensure contacting of the particles made of electrochemically active material among themselves and contacting to the current collector. Contacting problems are likely to occur, for example, due to gassing as a result of electrolyte decomposition or due to volumetric dynamics of particles during charging and discharging operations. The result of decontacting is often that electrodes cannot be discharged completely. This means that the theoretical energy content of an electrode is not depleted exhaustively.
DE 10 2009 023 126 A1 discloses a button cell, wherein the negative electrode is composed of zinc particles (the electrochemically active material), a particulate non-metallic conducting agent, and a binder. For production of such a button cell zinc powder, the non-metallic conducting agent, and the binder are extensively agitated in dry condition. The obtained powder is trickled into the cell lid of a button cell housing and an electrolyte is added. The cell lid is combined with an appropriate sealing and a matching cell cup including a cathode. Finally, the cell is closed.
In practice, that cell exhibited good to very good capacity values, in particular ascribed to good contacting of the zinc particles among themselves. These characteristics are attributed to the extensive dry intermingling of the electrode particles.
However, dry mixtures have a significant drawback. During processing of dry mixtures, there is a tendency toward segregation and, thus, to dehomogeneous distribution of the binder and the conducting agent in the electrode, in particular the size of the binder and conducting agent particles is greatly different from the size of the zinc particles.
There is thus a need to provide button cells that can be produced in a simple manner and exhibit a very high capacity.